1. Field of the Invention
The invention relates to precise pulse triggering means, particularly in the so-called DME (Distance Measuring Equipment).
2. Description of the Prior Art
The precise triggering of an electronic function is frequently necessary, and in DME the accuracy of range measurement is dependent upon precise triggering time. A DME system of the type is described in the text "Funksysteme fur Ortung und Navigation" by E. Kramar (Verlog Berliner Union GMBH, Stuttgart 1973), Pages 147 to 149.
The instant of triggering in a DME receiver is generally the point of time at which the first pulse of a DME pulse pair is half its maximum value. The following considerations refer only to the first DME pulse.
It frequently happens that the DME interrogation pulse (or reply pulse) reaches the DME transponder (or interrogator) not only by the direct path but is reflected from one or more obstacles and thus arrives at the DME transponder (or interrogator) also by an indirect path. The direct signals and the indirect signals are then superimposed on each other, and a pulse is obtained whose shape differs from that prescribed. If the instant of triggering continues to be derived in the manner described, an error will result caused by this multipath propagation.